The leaching of alumina from calcined kaolin clay with nitric acid has been studied and reported on by numerous investigators since at least about 1918. The patent and technical literature is replete with descriptions of the leaching of clay at the atmospheric boiling point or at superatmospheric pressures and correspondingly higher temperatures, techniques for removing iron from the resulting extracts, purification by crystallization of aluminum nitrate nonahydrate, the recovery of aluminum mononitrate, and the decomposition of the mononitrate to alumina with recovery of the nitric acid values for recirculation to the leaching step. Although the prior art teaches technically feasible individual operations for accomplishing each of the foregoing individual steps, when combined into a complete extraction/purification process the energy requirements for the variously conceived overall processes are so high that none has been exploited commercially and to the best of our knowledge, only one, the "Nuvalon" process, has ever been formally practiced.